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The measurement of cosmic distances is like a scaffold, where levels are built upon the structure below. To measure the distances to far galaxies, astronomers must calibrate their measurements using closer objects that we know the distance to; those in turn must be calibrated by closer objects still. As a result, if we are to trust the measurements we've made of the structure and expansion of the Universe, we'd better have really good measurements to nearby galaxies.

For that reason, astronomers have devoted a lot of effort to measuring the distance to the Milky Way's brightest satellite galaxy, Large Magellanic Cloud. Now G. Pietrzyński and colleagues have determined that galaxy's distance with unprecedented accuracy. By identifying a set of rare binary stars, their properties allowed the astronomers to measure their distances from Earth to 2.2 percent accuracy. These results will help refine the measurements on which cosmology is founded: the expansion rate of the Universe.

Distances within the Solar System can be measured a number of ways, including direct methods like radar ranging. With a truly accurate estimate of the size of Earth's orbit, astronomers can use parallax—the apparent displacement of stars in the sky as Earth orbits the Sun—to find the distances to stars in the Milky Way. Some stars are variable, changing brightness in a predictable way; these provide a means of measuring how far it is to neighboring galaxies.

These and other measurements allow astronomers to calibrate distances to galaxies containing Type Ia supernovae. These explosions are visible billions of light-years away, and outshine everything else in their host galaxies. As acknowledged by the 2011 Nobel Prize in physics, Type Ia supernovae are currently our best way to track the expansion rate of the Universe.

The current study provides a possible alternative means to measure distances on an intermediate scale with more accuracy than we can get using variable stars. The Large Magellanic Cloud (LMC) is the second-closest galaxy to the Milky Way; you can think of it as the second layer of scaffolding, above measurements inside our galaxy. (Only the Sagittarius dwarf spheroidal galaxy is closer than the LMC, but it's much smaller and fainter, and therefore less useful for cosmological calibrations.)

The researchers used data from the Optical Gravitational Lensing Experiment (yes, it's nicknamed OGLE), which was designed to look for fluctuations in dark matter density by observing stars in the LMC. While OGLE hasn't succeeded in its primary goal of spotting clumps of dark matter, it has amassed a lot of data from 35 million stars, going back as far as 1992.

From those 35 million stars, the astronomers identified 12 eclipsing binary stars; of those, they analyzed data from eight pairs for a period of eight years. These pairs they chose are rare, consisting of stars in the helium-burning stage, which occurs after they have exhausted their core's hydrogen fuel. Aging stars of this type have well-known intrinsic brightness in relation to their color.

The researchers also selected the eight binaries for the length of their orbits: relatively long periods ranging between 60 and 772 days. Combined with the amount of light blocked during the eclipses, these long orbits enabled the astronomers to reconstruct the sizes of the stars through the same techniques that are commonly used for spotting exoplanets. That provided a detailed physical picture of the binary star systems, pinpointing their exact intrinsic brightness to approximately 2 percent accuracy. If an object's intrinsic brightness is known, it's a remarkably simple matter to estimate its distance from Earth based on how much of that light reaches us.

The LMC has a fairly simple structure—a flattened disk—and all the binaries were found close to the galaxy's center. As a result, the astronomers used the stars' distances to estimate how far the LMC's center is from Earth: 49.97 kiloparsecs, give or take 0.19 kiloparsecs. (One kiloparsec is a thousand parsecs, or roughly 3,300 light-years.) That accuracy is about 2.2 percent, a vast improvement over previous estimates based on variable stars, which did no better than 8 percent.

With these estimates in hand, it will be possible to calibrate the expansion rate of the Universe—a quantity known as the Hubble parameter—to about 3 percent accuracy. Future observations should be able to improve both the LMC distance measurement and the Hubble parameter even further.

I'm confuddled why anyone at Ars would downvote fieyr when half the time the forums consist of arguments over methodology & semantics in the first place. I'm doubly confuddled no one dropped the oh-so-point-proving "[citation needed]" quotation.

I've always said that it IS conceivable he used the term correctly. If it were a particularly difficult-to-navigate part of space, being able to make the run in a shorter distance would be something to brag about. I know this isn't the LIKELY answer (we pretty much know it was just the usual case of misusing fancy-sounding words), but it is a plausible one.

fieyr wrote:

Because it is prone to misunderstanding. Just like saying a star burns is prone to misunderstanding for people whose everyday experience consists of burning of the non-nuclear variety. Also, I imagine things that you and I might consider as 'understood' are fairly annoying to someone trying to learn English.

tyrsius wrote:

fieyr wrote:

^We should probably stop doing that.

Why? Its perfectly understandable to most people. It doesn't need to be scientifically accurate, its understood.

English as a language in itself is prone to misunderstanding. There's a reason German was the language of philosophy for centuries: it's exceedingly precise and has excellent information density. As to your comment about learning Englisch, unless they were completely unfamiliar with what a star is or how it works (why are those people reading this article?), the intent and meaning would be rather clear. That right there is how you LEARN a language and how it's actually used. Learning from a book doesn't help worth a damn; go out to the pub and talk with people there to learn how a language is actually spoken.

Whatever your alleged intentions, it's very clearly pedantry for the sake of pedantry.

And to the other guy, no, they really don't need the horrific (and butchered) explanation of fusion. This is Ars Technica, not Fox, we know what fusion is, we know it's what stars do.

As someone who did work on nuclear reaction calculations in stellar conditions, we called it "burning" and used horrible terms like "flame fronts" "deflagration" and "detonation" for the nuclear-based reactions going on the hydrodynamic sims. We even called the module that did the nuclear calculations "the burner." When a star goes through different phases of reactions we call them "Carbon Burning" or "Silicon Burning" (with the semi-joke that when we do silicon burning, we really burn silicon).

Really, that's just how the language for the field goes, you shouldn't jump on the article writer for using the same language as the people doing the actual work.

Ah, this is incredible. I find the Cosmic Distance Ladder a fascinating subject in general, and figuring out ways to improve it with another layer of measurements on top of the others is fantastic!

I wonder how far out this method is useful. Since it requires observing individual stars, it seems like it'd be about as far as the Cepheid variables.

Oh, and for the record, sunburn is in fact a burn. UV doesn't just damage DNA, it damages tissues in multiple ways, and the result is a burn of almost exactly the same nature as that caused by heat. Which is unsurprising because that's what the UV ends up as once absorbed by your tissues. And is why a sun burn, just like any other burn, can continue causing damage even after you've come inside / taken your face off the skillet, as the heat continues to spread until it has dissipated enough.

Ah, this is incredible. I find the Cosmic Distance Ladder a fascinating subject in general, and figuring out ways to improve it with another layer of measurements on top of the others is fantastic!

I wonder how far out this method is useful. Since it requires observing individual stars, it seems like it'd be about as far as the Cepheid variables.

Oh, and for the record, sunburn is in fact a burn. UV doesn't just damage DNA, it damages tissues in multiple ways, and the result is a burn of almost exactly the same nature as that caused by heat. Which is unsurprising because that's what the UV ends up as once absorbed by your tissues. And is why a sun burn, just like any other burn, can continue causing damage even after you've come inside / taken your face off the skillet, as the heat continues to spread until it has dissipated enough.

Basically, it damages the DNA in skin cells, which triggers apoptosis; the sloughing of the skin is the dead cells falling off as they're replaced. While yes, one could argue (correctly) that thermal energy is a type of radiation, it is not the type of radiation that is causing a sunburn.

(if it makes you feel better, I was about to correct him as well, but I did my fact-checking before I would have had to eat my boot, and saw that he was, in fact, correct)